Add a negate option for each condition

We could start by adding a validation column in the table in ConditionsTable.php @ namespace Drupal\commerce_conditions_plus\Element;,

    $element['condition_plugins'] = [
      '#type' => 'table',
      '#header' => [
        ['data' => t('Condition name'), 'colspan' => 3],
        t('Settings'),
        t('Weight'),
+        t('Validation'),
        t('Operations'),
      ],
      '#tabledrag' => [
        [
          'action' => 'order',
          'relationship' => 'sibling',
          'group' => 'condition-order-weight',
        ],
      ],

And then add the wrapper and checkbox

      $condition_form['negate_wrapper'] = [
        '#type' => 'container',
        '#title' => t('Negate'),
      ];
      $condition_form['negate_wrapper']['negate'] = [
        '#type' => 'checkbox',
        '#title' => t('Negate condition'),
      ];

Of course the difficult part is figuring our how to tap into commerce core conditions and negate any condition.